Autism is a severe neuropsychiatric disorder affecting social, communicative, and compulsive/repetitive behaviors. It is often accompanied by significant aggression, self-injury, impulsivity, and mood instability, creating an even greater challenge for families or educational settings. Currently, there are no treatments approved by the Food and Drug Administration (FDA) for this disorder, though early intervention, including behavioral and educational therapies and medication, may play a role in treatment. Omega three fatty acids have been found to improve symptoms of both depression and aggression in a number of studies in mentally populations including individuals with Bipolar Disorder, Borderline Personality Disorder, as well as decreasing violence in a prison population. These essential fatty acids are safe and have not been shown to have any drug interactions. Anecdotal evidence suggests they may be helpful in treating mood and aggressive symptoms in autism as well. Indeed, fatty acid levels have been found to be decreased in children with autism. This study will provide preliminary data on the impact of Omega 3 fatty acids on the various aspects of autism. This study is an innovative treatment approach to autism. It adapts a promising adjunct therapy for bipolar disorder and schizophrenia to a new population, that of children and adolescents with autism. It will analyze the possible relationship between the dose of omega 3 fatty acids (docohexanoic acic and eisopentanoic acid) and treatment outcomes. Finally, it will attempt to identify which specific subgroup of subjects with autism will respond to this intervention, which components and associated features are most responsive and whether this impacts subjects' quality of life. The data generated by this study are intended to support the rationale for a full-scale, large multi-site clinical trial. The following are the specific aims for this study. 1.) To assess the effect of omega 3 fatty acids vs. placebo treatment on the global severity of child and adolescent autistic disorder; 2.) To assess the effect of omega 3 fatty acids vs. placebo treatment on symptoms of aggression and irritability associated with autism. 3.) To assess the effect of omega 3 fatty acids vs. placebo treatment on functional ability. These aims will be achieved through a double-blind placebo-controlled parallel clinical trial of 60 child or adolescent outpatients, comparing omega 3 fatty acids and placebo as adjuncts in the treatment of autistic disorder for 12 weeks of treatment. [unreadable] [unreadable] [unreadable]